Varicella-zoster virus (VZV) persists in a latent state in sensory ganglia and may later undergo reactivation. A current model of VZV latency postulates that the viral lytic cycle is suppressed by a down-regulatory VZV product, limiting virus production to a level that can be overcome by immune surveillance. Alterations in the balance between virus production and host immunity allow replication of virus in the ganglion which is subsequently manifested as clinical zoster. This proposal describes investigations of human dorsal root ganglia utilizing quantitative reverse transcription (RT)-polymerase chain reaction (PCR), in situ RNA hybridization, and in situ RT-PCR with the aim of identifying the genes involved in maintaining virus latency and the genes required for virus reactivation. We will identify genes that are expressed in tissue with latent and early reactivated virus. These genes will be cloned into bacterial vectors for in vitro mutagenesis and functional analysis. Mutant genes with functional significance will be used to construct recombinant viruses to be evaluated in vitro and in vivo utilizing the rat model of VZV latency and tissue culture systems. With this strategy, we will identify mutant viruses that are deficient in their reactivation potential. We thereby hope to develop vaccine candidates that could prevent both varicella and zoster.